Apparatus and method for planarizing a workpiece and a workpiece handling wand for use in the method

ABSTRACT

A work piece carrier head for the chemical mechanical planarization of a work piece includes a backing plate that is capable of being extended beyond the lower surface of the carrier head during a work piece loading operation. The exposed lateral surface of the backing plate in the extended position provides a reference surface to enable a work piece handling wand to align itself prior to loading the work piece into the carrier head. The work piece handling wand is configured to grip a work piece between a concave cradle and a moveable gripping finger. A work piece held by the wand can be centered relative to the backing plate prior to loading the work piece into the work piece carrier head by registering the wand to the exposed lateral surface of the extended backing plate.

FIELD OF THE INVENTION

[0001] This invention relates generally to a method and apparatus for planarizing a work piece, and more particularly to a method and apparatus for aligning a work piece to a planarization apparatus and to the planarization and work piece handling apparatus and method.

BACKGROUND OF THE INVENTION

[0002] The manufacture of many types of work pieces requires the substantial planarization of at least one surface of the work piece. Examples of such work pieces that require a planar surface include semiconductor wafers, optical blanks, memory disks, and the like. For example, integrated circuits are typically formed on substrates such as silicon wafers by the sequential deposition of conductive, semi-conductive, or insulating layers. After each layer is deposited, the layer is pattern etched to define circuit features. As the series of layers are sequentially deposited and etched, the device side of the substrate becomes progressively more non-planar. This non-planar surface presents a problem for the integrated circuit manufacturer. If the outer surface is sufficiently non-planar, the photolithographic technique used to pattern the layers become ineffective because the non-planar surface prevents proper focusing of the photolithographic apparatus over the entire surface of the substrate. Additionally, if the outer surface is sufficiently non-planar, subsequently deposited layers are unable to adequately cover the steps in the non-planar surface. There is a need, therefore, to planarize the substrate surface periodically to provide a planar surface on the device side of the wafer on which the photolithographic apparatus can focus and which can be covered adequately by the subsequently deposited layers.

[0003] Chemical mechanical planarization (CMP) is one accepted method of achieving a planar surface. The CMP method typically requires the work piece to be mounted on a carrier head with the surface to be planarized exposed. The exposed side of the work piece is then held against a moving polishing pad. In addition, the carrier head may oscillate and/or rotate about its own axis to provide additional motion between the work piece and polishing surface. A polishing slurry, including an abrasive and at least one chemically-reactive agent, is spread on the polishing pad to provide a mechanically abrasive as well as chemically reactive solution at the interface between the pad and the work piece surface.

[0004] A conventional carrier head for performing chemical mechanical planarization includes a circular work piece carrier plate having a diameter substantially equal to the diameter of the work piece to be polished. The carrier plate is compliantly mounted in the main housing of the carrier head to allow the plate to float relative to the carrier head during the planarization process. The back side of the carrier plate forms part of a wall of a chamber that can alternatively be pressurized in order to bias the work piece against the polishing pad or evacuated in order to retract the carrier plate into the head and to attract and retain the work piece against the carrier plate as explained hereinafter. The front surface of the carrier plate typically includes a compliant or elastomeric membrane film to provide some degree of compliance between the plate and the back surface of the work piece. The carrier plate also has a plurality of perforations passing through the plate into the chamber. An annular wear ring composed of a hard material such as ceramic is rigidly mounted to the main carrier head housing immediately radially outward of the rigid carrier plate.

[0005] In a conventional method, in order to load a work piece into the apparatus for planarization, a robotic arm equipped with a work piece handling wand picks up the work piece from a previous station, or from a work piece queue, and moves the work piece to a position directly beneath the work piece carrier head. The chamber within the work piece carrier head housing is evacuated, which has the effect of retracting the carrier plate into the carrier head housing and causing air to be drawn in through the perforations. The wand then moves the work piece into position on the carrier plate until the back side of the work piece contacts the front surface of the carrier plate thereby sealing the perforations in the plate. The vacuum thus created holds the work piece securely to the plate. A vacuum check may be performed to ensure that the work piece has been properly loaded into the work piece carrier head. The vacuum continues to hold the work piece in the carrier head as the wand is released and moved out of the way. The carrier head then moves down against the polishing pad until the wear ring is pressed against the pad, and the pad begins to rotate to begin the polishing process. The chamber behind the elastomeric membrane is pressurized to a predetermined level to force the work piece against the polishing pad during the polishing process. The work piece is maintained on center with respect to the carrier head by the cylindrical inside surface of the wear ring, which traps the work piece between the polishing pad and the plate. In order to maintain the precise control of the position of the work piece necessary for CMP, the clearance between the outside diameter of the work piece and the inside diameter of the wear ring must be kept to a minimum. For example, in the CMP processing of a 200 mm (8 inch) semiconductor wafer the clearance is typically less than 1 mm. This tight tolerance between the work piece and the wear ring poses substantial design challenges in terms of the necessity for highly accurate positioning of the work piece prior to loading the work piece in the carrier head. To accomplish reliable loading of the carrier head, the robotic arm must be able to pick up the 200 mm semiconductor wafer from the previous station and place it in the carrier head with a combined positional accuracy of less than 0.5 mm. A wafer that is out of position at the previous station when it is picked up by the robot arm and/or a robot tool point position that is out of position at the carrier head by more than a combined 0.5 mm will cause the wafer to be misloaded, leading to a stoppage in the throughput of the CMP apparatus. Worse, if a failure in the loading of the carrier head is not detected by the vacuum check, the wafer can slip between the wear ring and polishing pad, resulting in a total loss of the wafer. Similar positional accuracy is also required for other work pieces. In view of the foregoing, there is a need for a work piece planarization apparatus and method that provides reliable aligning of the work piece prior to initiation of the planarization operation. Further, there is a need for a work piece handling wand capable of aligning itself to a reference surface of the work piece carrier head to ensure proper alignment between the work piece and the carrier head prior to loading the work piece to the carrier head.

BRIEF DESCRIPTION OF THE DRAWING

[0006] The present invention will be better understood from a reading of the following detailed description, taken in conjunction with the accompanying drawing figures in which like references designate like elements, and in which:

[0007]FIG. 1 illustrates, in a partial diagrammatic cross-sectional view, a wafer carrier head incorporating features of the present inventions and illustrating the wafer carrier plate in the retracted position;

[0008]FIG. 2 illustrates, in a partial diagrammatic cross-sectional view, the wafer carrier head of FIG. 1 with the wafer carrier plate in the extended position;

[0009]FIG. 3 illustrates, in perspective view, a wafer-handling wand incorporating features of the present invention;

[0010]FIGS. 4 and 5 are portions of FIG. 2 enlarged to illustrate details of the wafer-handling wand;

[0011]FIG. 6A illustrates, in top view, the wafer-handling wand of FIG. 2;

[0012]FIG. 6B-6E illustrate, in top views, the wafer-handling wand of FIG. 2 shown holding wafers in various orientations;

[0013]FIG. 7 illustrates, in side view, an alternative embodiment of a wafer-handling wand incorporating features of the present invention;

[0014] FIGS. 8-10 illustrate, in cross sectional views, portions of work piece carrier wands in accordance with alternative embodiment of the invention; and

[0015]FIG. 11 illustrates, in a partial diagrammatic cross-sectional view, a portion of a work piece carrier head in accordance with a further embodiment of the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0016] In accordance with one embodiment of the invention, planarization apparatus is provided that facilitates the accurate loading of a work piece into the apparatus prior to the planarization operation. In accordance with one embodiment of the method invention, a work piece handling wand is used to convey a work piece to the planarization apparatus and to align the work piece to a work piece carrier head. Alignment is accomplished by bringing an alignment element on the work piece handling wand into contact with a reference surface on or combined with the work piece carrier head.

[0017] The drawing figures are intended to illustrate the general manner of construction and are not necessarily to scale. In the description and in the claims, the terms left, right, front, back, up, down, upper, lower, and the like are used for descriptive purposes. However, it is understood that the embodiment of the invention described herein is capable of operation in other orientations than as shown, and the terms so used are only for the purpose of describing relative positions and are interchangeable under appropriate circumstances. For purposes of illustration only, the invention will be described as it applies to a CMP apparatus and to a CMP process and specifically as they apply to the CMP processing of a semiconductor wafer. It is not intended, however, that the invention be limited to these illustrative embodiments; instead, the invention is applicable to a variety of planarization apparatus and to the planarization of many types of work pieces.

[0018]FIG. 1 illustrates, in a partial diagrammatic cross-sectional view, a wafer carrier head 10 in accordance with one embodiment of the present invention illustrating a wafer backing plate 34 in the retracted position. In addition to the wafer backing plate, wafer carrier head 10 includes a housing assembly 12 consisting of a main housing 14, a mounting ring 16 and a wear ring 18. Main housing 14 and mounting ring 16 are preferably made from a sturdy, rigid material such as stainless steel and wear ring 18 is preferably made of a hard, abrasive resistant material such as ceramic. Wafer carrier head 10 is supported for rotation about its axis 21 by bearing 20 and is driven by a conventional platen motor (not shown). Housing assembly 12 includes an inner bore 22 defined by the interior surfaces 24, 26, and 28 of main housing 14, mounting ring 16, and wear ring 18, respectively. Mounting ring 16 may be attached to main housing 14 by a plurality of threaded fasteners 30 or by other known fastening methods. Alternatively, the interior and exterior features of mounting ring 16 may be machined directly into main housing 14. Wear ring 18 is secured to main housing 14 by a plurality of threaded fasteners 32. Alternative methods of assembling the components of housing assembly 12 such as welding, brazing, adhesives, etc. are well-known in the art and are considered to be art recognized equivalents for the purpose of this disclosure.

[0019] Wafer-backing plate 34 is disposed in bore 22 of housing assembly 12. Wafer-backing plate 34 includes a lower-half plate 36 and an upper half plate 38 held together by conventional means such as a plurality of threaded fasteners 40. A diaphragm 42 comprising an annular disk of soft, flexible material such as polyurethane, neoprene impregnated Nylon, or other conventional elastomeric material is clamped between upper-half plate 38 and lower-half plate 36 and also between wear ring 18 and mounting ring 16. Diaphragm 42 seals a back side chamber 44 from the external environment while permitting wafer backing plate 34 to float in and out of bore 22 of housing assembly 12. Wafer backing plate 34 further includes an internal passageway 46. An inlet 57 opens into passageway 46 through the back side 53 of wafer backing plate 34. Passageway 46 provides fluid communication between inlet 57 and a plurality of apertures 48 and 50 that open through front surface 52 of wafer backing plate 34. Inlet 57, in turn, is connected via a conventional telescoping coupling 55 to a tube 59 that is connected to a source of pressurized fluid (not shown). As used herein, fluid refers to both liquids and gases and pressure refers to gauge pressure in pounds per square inch (psig.). Thus, a positive gauge pressure means the fluid pressure is above one atmosphere and a negative pressure means the fluid pressure is below one atmosphere. Tube 59 is connected to a source of pressure through a conventional rotating coupling (not shown).

[0020] When negative pressure is supplied through inlet 57, air is drawn through apertures 48 and 50 which tends to attract and retain a wafer 54 against front surface 52 of wafer backing plate 34. A thin layer 56 of flexible material such as DF-200 carrier film manufactured by Rodell, Inc. of Newark, Del. may be applied to front surface 52 to provide a controllable degree of compliance between wafer backing plate 34 and the back side 58 of wafer 54 and also to assist in sealing back side 58 of wafer 54 against apertures 48 and 50.

[0021] Upper-half plate 38 further includes a radially extending flange 60 that extends into a corresponding radial groove 62 defined by the interior surfaces of mounting ring 16 and wear ring 18. The upper surface 64 of radially extending flange 60 abuts the upper surface 66 of radial groove 62 to provide a limit stop limiting the upward motion of wafer backing plate 34.

[0022] With reference to FIG. 2, back side chamber 44 is also connected to a conventional source of pressurized fluid via a conventional rotating coupling (not shown). When a positive pressure is present in back side chamber 44, wafer backing plate 34 is urged downward until lower surface 76 of radially extending flange 60 abuts lower surface 78 of radial groove 62. With wafer backing plate 34 thus extended, lateral surface 80 of wafer backing plate 34 is exposed beyond lower surface 82 of wear ring 18 and hence beyond the lower surface of housing assembly 12. The lateral surface 80 of wafer backing plate is preferably substantially cylindrical having a diameter substantially equal to the diameter of wafer 54. Lateral surface 80 provides a reference surface for a self-centering wafer-handling wand, discussed more fully hereinafter. In the illustrative embodiment, lateral surface 80 extends 0.254 cm (0.100 inch) beyond lower surface 82, however, a wafer-backing plate that extends any distance below the wear ring, or a wear ring that retracts, sufficiently (as explained more fully below) to enable a self-centering wand to use the lateral surface 80 as a reference surface is considered within the scope of the present invention.

[0023] In a commonly used and conventional wafer carrier head the pressure in back side chamber 44 is communicated to the front surface 52 of wafer backing plate 34 by a plurality of perforations passing through the wafer backing plate. Unlike the conventional wafer carrier head, in accordance with one embodiment of the present invention, the wafer backing plate pressure in backside chamber 44 is decoupled from the wafer vacuum function necessary to load the wafer against wafer backing plate 34. As shown in the illustrative embodiment, with a positive pressure in backside chamber 44, the wafer backing plate will be extended downward. Simultaneously, a negative pressure can be applied to apertures 48 and 50 via tubing 59. This causes air to be drawn in through apertures 48 and 50, enabling the wafer to be chucked against wafer backing plate 34 while the wafer backing plate is in the downwardly extended position. A conventional wafer carrier head could not simultaneously extend the wafer carrier plate and chuck the wafer because a positive pressure in the back side chamber would cause air to blow out of the apertures in the wafer backing plate.

[0024]FIG. 3 illustrates, in perspective view, a wafer-handling wand 84 in accordance with one embodiment of the invention. FIGS. 4 and 5 further illustrate, in side view, aspects of wand 84. Wand 84 includes a base 86 having a fitting 88 adapted to be mounted to a standard robotic arm such as those commonly used in CMP equipment. The base of wand 84 includes a cradle portion 90 consisting of a floor portion 92 and a raised wall portion 94. The raised wall portion has a concave surface 116, the radius of curvature of which is sized to match the radius of curvature of wafer 54 (i.e. for handling a 200 millimeter diameter wafer, the radius of curvature of surface 116 is preferably about 100 millimeters). A pair of support rails 96 and 98 extend outwardly from base 86 and support a bracket 100 at the distal ends thereof. Bracket 100 holds a moveable gripping finger 104. Gripping finger 104 has a flat portion 130 and a raised wall portion 126. Raised wall portion 126 has a surface 128 that faces toward cradle portion 90. Gripping finger 104 also includes a pair of flanges 106 and 108 that ride on a track 102 formed in bracket 100. The flanges 106 and 108 and track 102 cooperate to allow gripping finger 104 to extend and retract toward and away from cradle portion 90. A conventional pneumatic actuator 110 actuates gripping finger 104 via an actuator rod 112 that extends from the actuator to the gripping finger. A position sensor 114 senses the location of gripping finger 104 by monitoring the position of actuator rod 112.

[0025] In operation, a wafer is picked up by wand 84 by extending gripping finger 104 initially to its outermost position, moving the wand 84 to a position immediately above or below the surface of the wafer to be picked up and then retracting gripping finger 104 in a direction toward cradle portion 90 using actuator 110 until the perimeter surface 74 of wafer 54 is pressed into raised wall 94 of cradle portion 90. Position sensor 114 provides a signal to a control mechanism (not shown) indicating whether the final position of gripping finger 104 is within the appropriate range. If a wafer pickup is missed, gripping finger 104 will over travel inwardly toward cradle portion 90. The over travel will be detected by position sensor 114, which in turn will signal the control system (not shown) so that appropriate action (such as alerting the operator or re-attempting the wafer pickup) can be taken.

[0026] In accordance with a preferred embodiment of the invention and as illustrated in FIG. 4 (with continued reference to FIG. 3), raised wall portion 94 of base 86 has an upright concave surface 116 that opens toward the distal end 118 of wand 84. Upright surface 116 is also canted outwardly at an angle φ relative to a plane normal to the longitudinal axis 120 of wand 84. Floor portion 92 of cradle 90 also slopes away from its junction 124 with surface 116 at an angle θ relative to longitudinal axis 120. In a preferred embodiment the angle formed by the raised wall portion and the floor portion is greater than 90°. The angular orientation of surface 116 and floor 92 relative to wafer 54 cooperate to urge wafer 54 into junction 124 between the upright surface and the floor portion and ensures that wafer 54 is held substantially by its outer perimeter 74, with little or no contact between wand 84 and either the back side 58 or device side 61 of wafer 54. Additionally, the overhanging portion 127 of surface 116 enables wand 84 to align itself with a wafer carrier reference surface that is slightly smaller in diameter than the diameter of wafer 54 and/or to align itself with a wafer carrier reference surface equal in diameter to wafer 54 while loosely holding wafer 54 along the sloping floor 92 of cradle portion 90.

[0027] With reference to FIG. 5 (and with continued reference to FIG. 3), surface 128 of the upright wall portion 126 of gripping finger 104 is also canted inwardly at an angle ψ relative to a plane normal to longitudinal axis 120. Floor portion 130 slopes away from junction 132 between surface 128 and floor portion 130 at an angle Ω relative to longitudinal axis 120. In a preferred embodiment the angle formed by the upright wall portion and the floor portion is greater than 90°. As with the angular relationships described with reference to FIG. 4, the angular relationships between surface 128 and floor 130 tend to urge wafer 54 into junction 132 such that wafer 54 is held securely by its perimeter surface 74 with little or no contact between wand 84 and either back side 58 or device side 61 of wafer 54. In operation, overhanging portion 140 of upright wall portion 126 will extend above the surface of wafer 54.

[0028] As illustrated in FIG. 6, standard wafers used in the semiconductor industry often have a flat 136 ground on one side of the wafer to use as an orientation reference. FIG. 6A schematically illustrates, in top view, a wafer handling wand 84 and the angle 134 subtended by surface 116 of raised wall portion 94. Preferably angle 134 is equal to slightly more than twice the arc subtended by the flat on a standard wafer. For a 200 millimeter wafer, angle 134 needs to be larger than about 60 degrees and is preferably about 100 degrees. FIGS. 6B-6E illustrate schematically the various possible positions of a wafer 54 and the associated flat 136 relative to the components of wafer handling wand 84. As shown in FIGS. 6B-6E, with angle 134 sized in accordance with the foregoing, irrespective of the orientation of the flat 136 of wafer 54, a wafer picked up by wand 84 will always be centered relative to cradle portion 90 of wand 84 even when, as shown in FIG. 6C, part of flat 136 overlaps the end 138 of edge 116.

[0029] With reference again to FIG. 2, operation in accordance with one embodiment of the invention will now be described. Once a wafer 54 has been picked up as described above, wand 84 moves wafer 54 to a position directly beneath wafer backing plate 34. Positive pressure is supplied to back side chamber 44 which causes wafer backing plate 34 to move to its fully extended position as shown in FIG. 2. Gripping finger 104 is then moved outward slightly so as to ensure overhanging portions 127 and 140 will clear the lateral surface 80 of wafer backing plate 34. Wand 84 is then moved upward toward wafer carrier head 10 until upper surfaces 142 and 144 of raised wall portion 94 and gripping finger 104, respectively, contact lower surface 82 of housing assembly 12. Alternatively, the robotic arm can be programmed to stop just short of making contact with lower surface 82, however, where vertical tolerances are critical, the interaction between upper surfaces 142 and 144 with lower surface 82 provide a reference surface that is substantially less likely to drift out of tolerance than even the best robotic arm tool point positioning capability. The vertical compliance of the wand and the robot arm links make it such that a wide variation in the vertical axis tool point can be successfully accommodated.

[0030] Once the vertical axis reference has been established, gripping finger 104 is urged inward by actuator 110 such that wand 84 grips wafer backing plate 34 between upright surfaces 116 and 128, thus centering wand 84 radially with respect to wafer carrier plate 34 in the same manner as wafer 54 itself was centered. Once wand 84 has been centered with respect to wafer backing plate 34, and with wafer backing plate still extended, negative pressure is supplied through tubing 59 to apertures 48 and 50 via internal passage 46 which draws the now centered wafer 54 up against front surface 52 of wafer backing plate 34. With the wafer now removed from wand 84, the wand can be retracted to allow the planarization process to be initiated. A vacuum check may be conducted to verify proper loading of wafer 54 and if a proper head load is indicated, negative pressure is then supplied to back side chamber 44 which retracts wafer backing plate 34 to its fully retracted position as shown in FIG. 1. A second vacuum check can be performed to verify wafer 54 was not dislodged during retraction of wafer backing plate 34. Thereafter, wafer carrier head 10 and with it wafer 54 move down to a predetermined position with lower surface 82 in contact with polishing pad 68. Positive pressure is then applied to backside cavity 44 which urges wafer backing plate 34 downward, biasing wafer 54 against polishing pad 68 as the prescribed motion of platen 70 is initiated. At the same time, wafer carrier head 10 may be caused to revolve or orbit around its own axis 21 to provide additional relative motion between the polishing pad and the wafer.

[0031] In accordance with one embodiment of the invention, wand 84 can be used again to remove wafer 54 from the carrier head when the planarization process is complete. After completing the planarization process, negative pressure is applied through tubing 59 to hold wafer 54 against wafer backing plate 34 as wafer carrier head 10 is withdrawn from polishing pad 68. As wafer carrier 10 is withdrawn, positive pressure remaining in back side cavity 44 causes wafer backing plate 34 to extend again to its fully extended position as shown in FIG. 2. Wand 84 is moved back into position with finger 104 extended. Finger 104 is then retracted to center wand 84 relative to lateral edge 80 of wafer backing plate 34. The pressure in tubing 59 is then changed from a negative pressure to a positive pressure, allowing wafer 54 to drop into wand 84. Wand 84 is withdrawn slightly to clear the end of wafer backing plate 34 (or alternatively wafer backing plate 34 is withdrawn into carrier head 10) and gripping finger 104 is retracted to grip wafer 54.

[0032]FIG. 7 illustrates, in cross section, an alternative embodiment of a wafer gripping wand 184 in accordance with a further embodiment of the invention. Wafer gripping wand 184 includes a cradle portion 290 having an upright wall 294 extending in a first direction substantially normal to longitudinal axis 220 and a movable gripping finger 204 disposed at the distal end 218. The operation and function of cradle portion 290 and gripping finger 204 are identical to the previously described operation and function of cradle portion 90 and gripping finger 104, respectively. On the reverse or lower side of the wand 184 there is second cradle portion 390 consisting of an upright raised wall 394 also extending substantially normal to longitudinal axis 220 but in a second direction substantially opposite that of upright wall portion 294. A movable gripping finger 304 also extending in the second direction is disposed at the distal end 218 of wand 184. Cradle portion 390 and gripping finger 304 are also identical in function to cradle portion 90 and gripping finger 104, respectively, as hereinbefore described. The two-sided configuration of wand 184 permits an increase in throughput of a wafer planarization apparatus. In operation, the two-sided wand 184 can pick a wafer from a station, such as a spray queue, and move it to the wafer carrier head 10. Before loading the wafer, however, the two-sided wand 184 is capable of picking up the previously planarized wafer (either from the polishing pad or the carrier head). The two-sided wand 184 can then rotate 180° about its axis 220 to load the wafer to be planarized into the wafer carrier head before returning to the spray queue with the planarized wafer. By handling two wafers at once, the two-sided wand 184 can unload and load sequential wafers without returning to the spray queue, thereby increasing throughput. Additionally, if the two-sided wand 184 is used to remove a planarized wafer from the carrier head, pad conditioning can occur from the moment the wafer carrier head is retracted from the polishing pad until the time the head is ready to begin another planarization cycle. This enables an even further increase in throughput.

[0033] FIGS. 8-10 each illustrate alternate embodiments of the invention for the centering of a work piece handling wand and the work piece gripped thereon with respect to a work piece carrier head. In accordance with these further embodiments of the invention, the work piece handling wand, and the work piece gripped thereon, can be properly centered with respect to the work piece carrier head by including on the wand a protrusion or plurality of protrusions that extends above the wand and contacts some repeatable physical reference surface on the carrier head. Using a wand having a protrusion in this manner avoids the necessity of registering to the lateral edge of the work piece backing plate to achieve proper location of the work piece. Indeed, when such a wand is used with a prior art work piece carrier head, centering of the wand against, for example, the wear ring would be a preferred method.

[0034]FIG. 8 illustrates, in cross section, a wafer-handling wand 484 that can be similar to wafer-handling wand 84 or wafer-handling wand 184, previously described, except for a protrusion 485 extending upwardly from base 486. In accordance with one variation of the invention, wafer handling wand 484 can also include, as illustrated, a protrusion 487 extending upwardly from gripping finger 404. Protrusion 485 can have a concave surface 489 that mates with an outer diameter 413 of housing assembly 412 of wafer carrier head 410. Protrusion 487, if included in the implementation, in operation, can be made to abut the opposite side of housing assembly 412.

[0035]FIG. 9 illustrates, in cross section, a portion of a wafer handling wand 584 in operative alignment with the edge of a wear ring 582. The wear ring, in turn, is an operative component of a wafer carrier head (not shown). Wand 584 can be similar to the previously described wafer handling wands except for a protrusion 585 extending upwardly from base 586 and a protrusion (not illustrated) that would extend upwardly from a gripping finger at the other extremity of the wand. Protrusion 585 can have a concave surface 589 that mates with the outer diameter of generally cylindrical wear ring 582. The wafer carried by wafer handling wand 584 is placed in proper alignment with the carrier head by bringing protrusion 585 into contact with the edge of the wear ring. Although not illustrated, as an alternative embodiment, wand 584 can be configured with a protrusion that mates with the generally cylindrical inner surface of wear ring 582.

[0036] The lower edge of the carrier head, and especially the outer edge of the wear ring may become covered, at least partially, by slurry and/or residue of the planarization process. These contaminants may interfere with the proper alignment of the wand and the wafer to the wafer backing plate when alignment relies on the wand protrusion contacting either of these contaminated surfaces. These potential alignment problems are overcome by a wafer handling wand 684 illustrated in FIG. 10. FIG. 10 illustrates, in cross section, a portion of wafer handling wand 684 in operative alignment with a protrusion 690 extending outwardly and downwardly from housing assembly 612 of a wafer carrier head 610. Protrusion 690 is located sufficiently high above the bottom surface of the wafer carrier head (and hence above the polishing pad) to avoid the above described contaminants. Wand 684 can be similar to the previously described wafer handling wands except for a protrusion 685 extending upwardly from base 686 and a protrusion (not illustrated) that would extend upwardly from a gripping finger at the other extremity of the wand. Protrusion 685 can have a shaped surface 689 that mates with a surface 692, having a complementary shape, of protrusion 690. The wafer carried by wafer handling wand 684 is placed in proper alignment with the carrier head by bringing protrusion 685 into contact with surface 692 of protrusion 690. The remaining steps of aligning a wafer to the wafer carrier head utilizing the inventive embodiments illustrated in FIGS. 8-10 can be similar to the steps described above in connection with the use of wafer handling wand 84.

[0037]FIG. 11 schematically illustrates, in cross section, a portion of a wafer carrier head 710 in accordance with a further embodiment of the invention. Mechanical portions of the carrier head that provide for motion of the carrier head, both vertical and rotary or oscillatory, and means for conveying fluids to the operative portion of the carrier head are not shown, but can be implemented in manner similar to those described above with respect to wafer carrier head 10. Wafer carrier head 710 includes a flexible web diaphragm 742 having a horizontal portion 744 against which a wafer 54 is positioned for planarization. Flexible web diaphragm 742 also includes a vertical portion 746 that terminates in a flange 748. Flange 748 can be securely fastened to a housing assembly 712 of wafer carrier head 710. The coupling can be effected by a rigid flange clamp 750 that is screwed or otherwise attached to the housing assembly. Rigid flange clamp 750 presses flexible web diaphragm flange 748 against housing assembly 712 sealing web diaphragm 742 against the housing assembly. The housing assembly and web diaphragm thus enclose a center chamber 752 within which the pressure can be controlled by the passage of fluid through an opening 754 that extends through the housing assembly to a pump or other pressure regulated supply (not shown). Although only one chamber is illustrated, the carrier head can include a plurality of chambers for controlling the pressure exerted against various regions of wafer 54 during the planarization operation.

[0038] In accordance with one embodiment of the invention, as further illustrated in FIG. 11, an edge chamber 756 is also formed in the housing assembly in alignment with flange 748. Rigid flange clamp 750 presses flange 748 against housing assembly 712 creating and sealing the edge chamber. An opening 758 extending through the housing assembly to edge chamber 756 allows control of the pressure within the edge chamber. By controlling the pressure within edge chamber 756, the vertical positioning of the vertical portion of the flexible web diaphragm can be controlled. This, in turn, controls the pressure exerted on the edge region of wafer 54 during the planarization operation.

[0039] In accordance with a further embodiment of the invention, also illustrated in FIG. 11, wafer carrier head 710 also includes a wear ring 718 positioned to surround wafer 54 during a planarization operation. Wear ring 718 is flexibly coupled to and suspended from housing assembly 712 by a flexible wear ring diaphragm 760. Wear ring diaphragm 760 is clamped to the housing assembly by a clamp 762 and to the wear ring by a wear ring clamp 764. The clamps can be attached by screw fasteners (not shown) or the like. The wear ring diaphragm and the housing assembly together form a wear ring chamber 766. An opening 768 through housing assembly 712 couples to a pressure supply (not shown) by which the pressure in the wear ring chamber can be controlled. By controlling the pressure in the wear ring chamber, the vertical position of the wear ring can be controlled. Wear ring 718 is illustrated in the lowered position, which is the position for the wear ring during the actual planarization operation. In this position the lower surface 772 of the wear ring is substantially coplanar with the surface of the wafer that is to be planarized. In accordance with one embodiment of the invention, the wear ring can be raised to an elevated position indicated by the dashed line 770 during a wafer load operation. In the elevated wear ring position, the lateral edge 780 of the flexible web diaphragm is exposed. That is, bottom 772 of wear ring 718 is above horizontal portion 744 of the flexible web diaphragm. Exposed lateral edge 780 can be used as a reference surface for properly positioning a wafer using a wafer handling wand such as wand 84 in the same manner as illustrated in FIG. 2. Stops (not illustrated) can be provided as part of the wear ring or wear ring clamp and also as part of the housing assembly to limit the vertical travel of the wear ring. Advantageously, the pressure in center chamber 752, edge chamber 756, and wear ring chamber 766 can all be independently controlled.

[0040] In accordance with yet a further embodiment of the invention, a reference band 774 can be attached to lateral edge 780 to provide a more reliable reference surface as illustrated in FIG. 11. Reference band 774 can be formed, for example, from stainless steel, polyethylene terephthlate (PET), polyetheretherketone (PEEK), or other rigid, chemically resistant material. The term “chemically resistant” implies the material is resistant to the chemicals commonly used in the planarizing process such as the chemical reagents in the slurry. The use of a reference band is most advantageous when the flexible web diaphragm, and especially the vertical portion of the diaphragm are made of a relatively soft material.

[0041] Thus it is apparent that there has been provided a method and apparatus for planarizing a work piece and a work piece handling wand for use in that process that fully meet the needs set forth above. Although certain preferred embodiments and methods have been disclosed herein, it will be apparent from the foregoing disclosure to those skilled in the art that variations and modifications of such embodiments and methods may be made without departing from the spirit and scope of the invention. For example, although in the foregoing description of the various embodiments of the invention reference has been made to the chemical mechanical planarization of semiconductor wafers, the invention is not to be so limited. As is readily apparent, the invention can be applied to planarization by other methods and to planarization of other generally flat, disk shaped work pieces. Additionally, although reference has been made to two specific types of carrier heads (the first generally referred to as a back surface referenced carrier head and the second generally referred to as a front surface referenced carrier head) those of skill in the art will recognize that the embodiments of the invention disclosed herein are applicable to carrier heads and planarization apparatus of various other designs. Accordingly, it is intended to include within the broad spirit of the invention all such variations and modifications as fall within the scope of the appended claims. 

What is claimed is:
 1. Apparatus for planarizing a surface of a work piece comprising: a work piece carrier housing having a first surface and a bore extending inwardly from the first surface of the housing; a plate slidably disposed within the bore, the plate having a front surface and a back surface, the front surface facing outwardly from the work piece carrier housing, the plate being moveable axially within the bore between an extended position in which the front surface extends beyond the first surface and a retracted position in which the front surface is retracted to a position above the first surface; an internal passage within the plate; and at least one aperture opening extending from the front surface to the internal passage and providing fluid communication between the at least one aperture and a source of pressurized fluid.
 2. The apparatus of claim 1 further comprising: a chamber formed by the back surface of the plate and the bore; and a source of pressurized fluid configured to communicated with the chamber and capable of urging the plate between the extended and retracted positions by fluid pressure in the chamber.
 3. The apparatus of claim 2, further comprising: an elastomeric diaphragm extending between the plate and the work piece carrier housing forming a flexible seal between the bore and the plate.
 4. The apparatus of claim 1 further comprising: a rigid mechanical limit stop operatively engaging the plate for positively limiting axial motion of the plate between the extended position and the retracted position.
 5. The apparatus of claim 4 wherein the rigid mechanical limit stop comprises: a radially extending groove formed in the bore; and a radially extending flange formed in the plate, the radially extending flange extending into the radially extending groove, the flange and groove cooperating to provide an upper limit stop and a lower limit stop to limit axial motion of the plate relative to the bore.
 6. The apparatus of claim 1 further comprising: a bearing supporting the housing for rotation about an axis parallel to the bore; and a motor coupled to the housing for rotating the housing about the axis.
 7. The apparatus of claim 1 further comprising a lateral surface extending between the front surface and the back surface, at least a portion of the lateral surface being exposed beyond the first surface when the plate is in the extended position.
 8. The apparatus of claim 7 wherein the lateral surface comprises a circular cross section having a diameter dimension substantially equal to a diameter dimension of the work piece.
 9. The apparatus of claim 8 further comprising a work piece handling wand configured to convey a work piece to a position proximate the front surface.
 10. The apparatus of claim 9 wherein the work piece handling wand comprises: a cradle portion; and a movable finger portion spaced apart from the cradle portion.
 11. The apparatus of claim 10 wherein the cradle portion comprises a raised wall portion having a concave surface with a radius of curvature substantially equal to a diameter dimension of the work piece.
 12. The apparatus of claim 11 wherein the movable finger portion comprises a raised wall portion.
 13. The apparatus of claim 12 wherein the movable finger portion comprises a movable finger portion slideably coupled to the cradle portion on a support rail.
 14. The apparatus of claim 13 wherein the movable finger portion is coupled to an actuator configured to move the movable finger portion on the support rail.
 15. The apparatus of claim 14 wherein the movable finger portion is configured to move on the support rail to a position spaced apart from the cradle portion by a distance substantially equal to the diameter of the work piece.
 16. The apparatus of claim 14 wherein the movable finger portion is configured to move on the support rail to a position spaced apart from the cradle portion by a distance substantially equal to the diameter of the circular cross section of the lateral surface.
 17. The apparatus of claim 14 further comprising a position sensor configured to sense the location of the movable finger portion.
 18. The apparatus of claim 10 wherein the work piece handling wand further comprises a protrusion extending from the cradle portion and configured to contact a physical reference surface on the work piece carrier housing.
 19. The apparatus of claim 18 further comprising a wear ring positioned to surround the bore and wherein the physical reference surface comprises a surface of the wear ring.
 20. The apparatus of claim 18 wherein the physical reference surface comprises a protrusion extending from the work piece carrier housing.
 21. Apparatus for planarizing a surface of a work piece comprising: a work piece carrier housing; a flexible diaphragm coupled to the work piece carrier housing, the flexible diaphragm comprising a horizontal portion against which a work piece can be positioned for planarization and a vertical portion having a substantially cylindrical shape extending upwardly from the horizontal portion; and a wear ring having a lower surface, a substantially cylindrical inner surface, and a substantially cylindrical outer surface, the wear ring flexibly mounted to the work piece carrier housing and surrounding the flexible diaphragm, the wear ring configured to be moveable between a lowered position in which the lower surface is substantially coplanar with the surface of the work piece and a raised position in which at least a portion of the vertical portion is exposed.
 22. The apparatus of claim 21 further comprising a work piece handling wand configured to convey a work piece to a position proximate the horizontal portion.
 23. The apparatus of claim 22 wherein the work piece handling wand comprises: a cradle portion; and a movable finger portion spaced apart from the cradle portion.
 24. The apparatus of claim 23 wherein the cradle portion comprises a raised wall portion having a concave surface with a radius of curvature substantially equal to a diameter dimension of the substantially cylindrical shape of the vertical portion.
 25. The apparatus of claim 24 wherein the movable finger portion comprises a raised wall portion.
 26. The apparatus of claim 25 wherein the movable finger portion comprises a movable finger portion slideably coupled to the cradle portion on a support rail and configured to move to a position spaced apart from the cradle portion by a distance substantially equal to the diameter of the work piece.
 27. The apparatus of claim 25 wherein the movable finger portion comprises a movable finger portion slideably coupled to the cradle portion on a support rail and configured to move to a position spaced apart from the cradle portion by a distance substantially equal to the diameter of the substantially cylindrical shape of the vertical portion.
 28. The apparatus of claim 23 wherein the work piece handling wand further comprises a protrusion extending from the cradle portion and configured to contact a physical reference surface on the work piece carrier housing.
 29. The apparatus of claim 28 wherein the physical reference surface comprises a protrusion extending from the work piece carrier housing.
 30. The apparatus of claim 23 wherein the work piece handling wand further comprises a protrusion extending from the cradle portion and configured to contact the substantially cylindrical inner surface of the wear ring.
 31. The apparatus of claim 23 wherein the work piece handling wand further comprises a protrusion extending from the cradle portion and configured to contact the substantially cylindrical outer surface of the wear ring.
 32. The apparatus of claim 23 wherein the substantially cylindrical shape of the vertical portion provides a reference surface to which the cradle portion can be aligned.
 33. The apparatus of claim 21 further comprising a reference band attached to the vertical portion of the flexible diaphragm.
 34. A work piece handling wand for moving a substantially circular work piece to and in alignment with a planarizing apparatus, the work piece handling wand comprising: a cradle portion; a movable finger portion spaced apart from the cradle portion at the distal end of a longitudinal axis extending from the cradle portion to the movable finger portion, the cradle portion and the finger portion configured to confine a work piece therebetween; and a reference surface configured to register with a reference surface on the planarizing apparatus to position the work piece in alignment with the planarizing apparatus.
 35. The work piece handling wand of claim 34 wherein the cradle portion comprises: a raised wall portion having a concave surface with a radius of curvature substantially equal to the curvature of the substantially circular work piece; and a substantially flat floor portion intersecting with the raised wall portion.
 36. The work piece handling wand of claim 35 wherein the raised wall portion is angled toward the longitudinal axis at an angle of less than 90° with respect to the longitudinal axis.
 37. The work piece handling wand of claim 36 wherein the substantially flat floor portion is angled away from the longitudinal axis.
 38. The work piece handling wand of claim 35 wherein the reference surface comprises the raised wall portion on the cradle portion.
 39. The work piece handling wand of claim 34 wherein the reference surface comprises a protrusion extending outwardly from the cradle portion.
 40. The work piece handling wand of claim 34 further comprising: a second cradle portion; and a second movable finger portion spaced apart from the second cradle portion at the distal end of the longitudinal axis, the second cradle portion and second movable finger portion positioned on the opposite side of the longitudinal axis from the cradle portion and the movable finger portion.
 41. A method for planarizing a work piece utilizing a work piece planarizing apparatus comprising a work piece carrier head, a wear ring, and a work piece carrier plate mounted therewith, the work piece carrier plate movable in a vertical direction from a retracted position to an extended position, the work piece carrier plate having a substantially planar surface with a plurality of apertures therethrough and a lateral edge, the lateral edge exposed when the work piece carrier plate is positioned in the extended position, and the wear ring positioned to surround the work piece carrier plate when the work piece carrier plate is positioned in the retracted position, the method comprising the steps of: positioning the work piece carrier plate in the extended position; transporting a work piece to a position proximate the substantially planar surface; drawing fluid through the plurality of apertures; and positioning the work piece in contact with the substantially planar surface so the fluid drawn through the plurality of apertures attracts and holds the work piece to the substantially planar surface.
 42. The method of claim 41 wherein the step of transporting comprises the step of transporting the work piece on a work piece handling wand.
 43. The method of claim 42 wherein the step of positioning the work piece comprises the step of centering the work piece relative to the work piece carrier plate by engaging a surface of the work piece handling wand with a surface of the work piece carrier head.
 44. The method of claim 42 wherein the step of positioning the work piece comprises the step of centering the work piece relative to the work piece carrier plate by engaging a surface of the work piece handling wand with the lateral edge of the work piece carrier plate.
 45. The method of claim 42 wherein the step of positioning the work piece comprises the step of centering the work piece relative to the work piece carrier plate by engaging a surface of the work piece handling wand with a surface of the wear ring.
 46. The method of claim 42 wherein the step of centering the work piece relative to the work piece carrier plate comprises the step of engaging a surface of the work piece handling wand with an outer diameter surface of the wear ring.
 47. The method of claim 42 wherein the step of centering the work piece relative to the work piece carrier plate comprises the step of engaging a surface of the work piece handling wand with an inner diameter surface of the wear ring.
 48. The method of claim 42 wherein the step of centering the work piece relative to the work piece carrier plate comprises the step of engaging a surface of the work piece handling wand with an alignment feature coupled to the work piece carrier head.
 49. The method of claim 42 wherein the step of transporting comprises the step of gripping the work piece between a raised cradle portion of the work piece carrier wand and a movable gripping finger of the work piece carrier wand position at a distal end of the work piece carrier wand.
 50. The method of claim 41 further comprising the steps of: moving the work piece carrier plate to the retracted position; and lowering the work piece carrier head to place the work piece in contact with a polishing pad.
 51. A method for planarizing a work piece utilizing a work piece planarizing apparatus comprising a work piece carrier head, a flexible work piece support diaphragm coupled to the work piece carrier head, and a wear ring flexibly mounted to the work piece carrier head and surrounding the flexible work piece diaphragm, the method comprising the steps of: retracting the wear ring to expose a lateral edge of the flexible work piece diaphragm; centering a work piece to be polished in alignment with the flexible work piece diaphragm; lowering the wear ring to position a lower surface thereof substantially coplanar with the work piece; and lowering the work piece carrier head to place the work piece in contact with a polishing pad.
 52. The method of claim 51 wherein the step of centering comprises the steps of: gripping the work piece with a work piece handling wand; and engaging a surface of the work piece handling wand with the lateral edge.
 53. A method for planarizing a work piece utilizing a work piece handling wand and a work piece planarizing apparatus comprising a work piece carrier head, a work piece support surface coupled to the work piece carrier head, and a wear ring coupled to the work piece carrier head and surrounding the work piece support surface, the method comprising the steps of: gripping a work piece with the work piece handling wand; aligning the work piece handling wand and the work piece to the work piece support surface; transferring the work piece from the work piece handling wand to the work piece support surface; and lowering the work piece carrier head to press the work piece into contact with a polishing surface.
 54. The method of claim 53 wherein the step of aligning comprises the step of engaging a surface of the work piece handling wand with a surface of the work piece carrier head.
 55. The method of claim 53 wherein the step of aligning comprises the step of engaging a surface of the work piece handling wand with a surface of the wear ring.
 56. The method of claim 53 further comprising the step of raising the wear ring to expose a lateral surface of the work piece support surface.
 57. The method of claim 56 wherein the step of aligning comprises the step of engaging a surface of the work piece handling wand with the lateral surface of the work piece support surface.
 58. The method of claim 56 wherein the work piece handling wand comprises a concave raised cradle portion and a moveable gripping finger adapted for gripping a work piece and wherein the step of aligning comprises the step of gripping the lateral surface of the work piece support surface between the concave raised cradle portion and the moveable gripping finger.
 59. A work piece handling wand for picking and placing a work piece having a thin, substantially circular disk shape, the wand comprising: an elongate frame having a proximal end and a distal end; a cradle portion coupled to the proximal end, the cradle portion comprising a first floor portion and a first raised wall portion, the first raised wall portion having a concave surface opening in the distal direction, the concave surface having a radius of curvature sized to substantially match the radius of curvature of the work piece; a gripping finger slidably coupled to the distal end and moveable toward and away from the proximal end, the gripping finger comprising a first base portion and a second raised wall portion, the second raised wall portion having a surface facing toward the cradle portion; and an actuator mounted to the frame and attached to the gripping finger for moving the gripping finger toward and away from the proximal end.
 60. The work piece handling wand of claim 59 further comprising a sensor capable of determining the position of the gripping finger relative to the proximal end.
 61. The work piece handling wand of claim 59 wherein the top of the first raised wall portion of the cradle portion is canted toward the distal end.
 62. The work piece handling wand of claim 61 wherein the first floor portion of the cradle portion extends away from the first raised wall portion at an angle greater than ninety degrees.
 63. The work piece handling wand of claim 59 wherein the concave surface subtends an angle of at least sixty degrees.
 64. The work piece handling wand of claim 59 wherein the concave surface subtends an angle of at least one hundred degrees.
 65. The work piece handling wand of claim 59 wherein the cradle portion and the gripping finger are disposed on a first side of the elongate frame and the first and second raised wall portions thereof extend in a first direction, the work piece handling wand further comprising: a second cradle portion coupled to the proximal end on a second side of the elongate frame opposite the first side, the second cradle portion comprising a second floor portion and a third raised wall portion having a concave surface opening in the distal direction, the third raised wall portion extending in a second direction opposite the first direction; a second gripping finger slidably coupled to the distal end on the second side, the second gripping finger comprising a second base portion and a fourth raised wall portion, the fourth raised wall portion having a surface facing toward the second cradle portion, the fourth raised wall portion extending in the second direction; and a second actuator mounted on the elongate frame and attached to the second gripping finger and capable of moving the second gripping finger toward and away from the second cradle portion.
 66. A method for planarizing a work piece by a process of chemical mechanical planarization comprising the steps of: moving a work piece handling wand comprising a cradle having a raised concave wall portion with a radius of curvature substantially the same as the radius of curvature of the work piece and a moveable gripping finger having a raised wall portion and adapted for movement toward and away from the cradle to a position proximate the work piece; moving the raised wall portion of the moveable gripping finger away from the raised concave wall portion of the cradle a distance greater than the diameter of the work piece; positioning the work piece handling wand such that the work piece is between the raised wall portion of the moveable gripping finger and the concave wall portion of the cradle; and moving the moveable gripping finger toward the cradle until the work piece is gripped between the raised wall portion of the moveable gripping finger and the concave wall portion of the cradle.
 67. The method of claim 66 further comprising the step of sensing the position of the moveable gripping finger to confirm that a work piece has been gripped.
 68. The method of claim 66 further comprising the steps of: moving the work piece handling wand and the work piece gripped thereby to a location proximate a work piece carrier head of a chemical mechanical planarization apparatus, the work piece carrier head having a reference surface of substantially circular cross section; moving the moveable gripping finger away from the cradle to increase the distance between the raised wall portion of the moveable gripping finger and the concave wall portion of the cradle whereby the increased distance is greater than the diameter of the substantially circular cross section of the reference surface; moving the work piece handling wand toward the reference surface until at least a portion of the reference surface is positioned between the raised wall portion of the moveable gripping finger and the concave wall portion of the cradle; and moving the moveable gripping finger toward the cradle until the reference surface is gripped between the raised wall portion of the moveable gripping finger and the concave wall portion of the cradle.
 69. The method of claim 68 further comprising the step of transferring the work piece from the work piece handling wand to the work piece carrier head while the reference surface is gripped between the raised wall portion of the moveable gripping finger and the concave wall portion of the cradle.
 70. The method of claim 68 further comprising the step of retracting a wear ring of the chemical mechanical planarization apparatus to expose the reference surface.
 71. The method of claim 66 further comprising the steps of: moving the work piece handling wand and the work piece gripped thereby to a location proximate a work piece carrier head of a chemical mechanical planarization apparatus, the work piece carrier head having a wear ring coupled thereto, the wear ring having a substantially cylindrical lateral outer surface; and centering the work piece relative to the work piece carrier head by engaging a projection extending from the cradle with the lateral outer surface.
 72. The method of claim 66 further comprising the steps of: moving the work piece handling wand and the work piece gripped thereby to a location proximate a work piece carrier head of a chemical mechanical planarization apparatus, the work piece carrier head having a wear ring coupled thereto, the wear ring having a substantially cylindrical lateral inner surface; and centering the work piece relative to the work piece carrier head by engaging a projection extending from the cradle with the lateral inner surface.
 73. The method of claim 66 further comprising the steps of: moving the work piece handling wand and the work piece gripped thereby to a location proximate a work piece carrier head of a chemical mechanical planarization apparatus, the work piece carrier head having a reference surface; and centering the work piece relative to the work piece carrier head by engaging a surface of the work piece handling wand with the reference surface. 